High temperature hybridized molecular functional group adhesion barrier coating and method

ABSTRACT

There is provided a high temperature hybridized molecular functional group adhesion barrier coating for a composite structure. The coating has one or more hybridized molecular functional groups attached to a composite surface of the composite structure, wherein the one or more hybridized molecular functional groups are hybridized through a chemical derivatization process. The coating further has one or more chemical derivatization compounds attached to the one or more hybridized molecular functional groups via a condensation reaction. The coating is resistant to high heat temperatures in a range of from about 350 degrees Fahrenheit to about 2000 degrees Fahrenheit, and the coating is a thermally protective, toughened adhesion coating that mitigates effects of a hostile operating environment.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of and claims priority topending application Ser. No. 13/421,838, filed Mar. 15, 2012, entitledHIGH TEMPERATURE HYBRIDIZED MOLECULAR FUNCTIONAL GROUP ADHESION BARRIERCOATING AND METHOD, the entire contents of which is incorporated hereinby reference, and which is a continuation-in-part application of U.S.Patent Application Ser. No. 13/069,373, filed on Mar. 22, 2011, now U.S.Pat. No. 8,764,929, entitled METHOD OF PROMOTING ADHESION AND BONDING OFSTRUCTURES AND STRUCTURES PRODUCED THEREBY, which is incorporated hereinby reference in its entirety.

BACKGROUND

1) Field of the Disclosure

The disclosure relates generally to methods for bonding of structures,and more particularly, to methods for promoting adhesion and bonding ofcomposite and metal structures, and the bonded structures producedthereby, such as for use in aircraft, spacecraft, and other vehicles andstructures. Further, this disclosure relates generally to barriercoatings and methods for application of barrier coatings, and moreparticularly, to high temperature adhesion barrier coatings and methodsfor application of such high temperature adhesion barrier coatings.

2) Description of Related Art

Composite and metal structures or component parts are used in a widevariety of applications, including in the manufacture of aircraft,spacecraft, rotorcraft, watercraft, automobiles, trucks, and othervehicles and structures. In particular, in aircraft construction,structures or component parts, such as composite structures or componentparts, are used in increasing quantities to form the fuselage, wings,tail section, and other component parts of the aircraft. Suchlarge-sized structural aircraft components may be manufactured bybonding together composites to composites, composites to metals, andmetals to metals.

Known methods and systems for bonding composite and metal componentparts together, such as aircraft component parts, typically involveusing fastener devices, such as bolts, screws, pins, or other fastenerdevices to secure the component parts together. However, using suchknown fastener devices can add to the overall weight of the aircraft,which can, in turn, increase fuel costs. Further, using such knownfastener devices can take time and labor to install and can requireprocurement and storage of the fastener devices, which can, in turn,increase installation, labor, and manufacturing costs.

In addition, known methods and systems for bonding composite and metalcomponent parts together, such as aircraft component parts, typicallyalso involve using film adhesives to join or bond two compositematerials together, two metal materials together, or a compositematerial to a metal material. In order to form the large-sizedstructural component, the components are firstly positioned and alignedwith respect to one another on a suitable supporting structure, inaccordance with previously known methods. The adhesive films aretypically applied in advance between the components which are to beadhesively bonded to one another. To improve structural bonding, knownmethods exist for modifying the surface of the composite or metalstructure or part prior to applying the adhesive. Known surfacemodification methods may require the roughening of the composite ormetal surface via sanding or grit blasting. Such known procedures cancreate some active oxide functional groups on the surface. However, itis believed that no known methods or systems exist for durable surfacemodification for improved structural bonding and for identifyingfunctional groups which have an affinity to enhance durable andsustainable structural bonding and thereby improve secondary bondingforces (Van der Waals forces) and which can, in turn, increase thedurable, long-term life of a composite bonded joint.

In addition, high temperature barrier coatings for composite and metalstructures are known. Such known high temperature barrier coatings maycomprise primers for structures. However, such primers may form thickfilms, such as thick adhesion promoters or corrosion prevention layers,which may be more sensitive to the thickness of the deposited film andmay be too thick, and which may, in turn, affect mechanical performanceof the structure. Moreover, such primers may form films that may be toothin, and which may, in turn, cause the film to be ineffective.

Attempts at durable high temperature surface modification for improvedhigh temperature structural adhesion barrier coatings under hostileoperating environments have been made. For example, typical knownprocesses require the roughening of the composite or metallic surfacevia sanding or grit blasting to mitigate possible exfoliation. However,such processes may create some active oxide on the surface but not tothe extent that the oxide groups themselves affect the thermal oxidativestability (TOS) of the structural members.

Moreover, attempts have been made to produce high temperature barriercoatings that can provide adhesion promotion for structural bonding andminimize thermal oxidative degradation. However, such attempts mayimpact structure life, damage tolerance, and durability, and may notsustain the structure under high temperature, hostile operatingenvironments.

Accordingly, there is a need in the art for methods and systems forpromoting adhesion and bonding of composite and metal structures thatprovide advantages over known methods and systems. Moreover, there is aneed in the art for high temperature adhesion barrier coatings andmethods that provide advantages over known coatings and methods.

SUMMARY

This need for methods and systems for promoting adhesion and bonding ofcomposite and metal structures is satisfied. Moreover, this need forhigh temperature adhesion barrier coatings and methods is satisfied. Asdiscussed in the below detailed description, embodiments of the methodsand systems may provide significant advantages over existing methods,coatings, systems, and devices.

In an embodiment of the disclosure, there is provided a high temperaturehybridized molecular functional group adhesion barrier coating for acomposite structure. The coating comprises one or more hybridizedmolecular functional groups attached to a composite surface of thecomposite structure, wherein the one or more hybridized molecularfunctional groups are hybridized through a chemical derivatizationprocess. The coating further comprises one or more chemicalderivatization compounds attached to the one or more hybridizedmolecular functional groups via a condensation reaction. The coating isresistant to high heat temperatures in a range of from about 350 degreesFahrenheit to about 2000 degrees Fahrenheit, and the coating is athermally protective, toughened adhesion coating that mitigates effectsof a hostile operating environment.

In another embodiment of the disclosure, there is provided a hightemperature hybridized molecular functional group adhesion barriercoating for a metal structure. The coating comprises one or morehybridized molecular functional groups attached to a metal surface ofthe metal structure, wherein the one or more hybridized molecularfunctional groups are hybridized through a chemical derivatizationprocess. The coating further comprises one or more chemicalderivatization compounds attached to the one or more hybridizedmolecular functional groups via a condensation reaction. The coating isresistant to high heat temperatures in a range of from about 350 degreesFahrenheit to about 2000 degrees Fahrenheit, and the coating is athermally protective, toughened adhesion coating that mitigates effectsof a hostile operating environment.

In another embodiment of the disclosure, there is provided a hightemperature hybridized molecular functional group adhesion barriercoating for a ceramic structure. The coating comprises one or morehybridized molecular functional groups attached to a ceramic surface ofthe ceramic structure, wherein the one or more hybridized molecularfunctional groups are hybridized through a chemical derivatizationprocess. The coating further comprises one or more chemicalderivatization compounds attached to the one or more hybridizedmolecular functional groups via a condensation reaction. The coating isresistant to high heat temperatures in a range of from about 350 degreesFahrenheit to about 2000 degrees Fahrenheit, and the coating is athermally protective, toughened adhesion coating that mitigates effectsof a hostile operating environment.

In another embodiment of the disclosure, there is provided a method ofpromoting adhesion on a composite surface. The method comprisesproviding a composite structure having at least one composite surface tobe bonded. The method further comprises preparing the at least onecomposite surface. The method further comprises providing a chemicalderivatization compound containing active functional groups that promoteadhesion. The method further comprises depositing the chemicalderivatization compound on the prepared composite surface to form afunctional group-adhesive promoter derivatized layer. The method furthercomprises applying an adhesive layer to the derivatized layer. Themethod further comprises heat curing the adhesive layer to result in abond with another structure made of a composite, a metal, or acombination thereof.

In another embodiment of the disclosure, there is provided a method forstructural bonding of structures. The method comprises providing a firststructure made of a composite material and a second structure made of acomposite material, a metal, or a combination thereof. The methodfurther comprises preparing a surface to be bonded on each of the firstand second structures to form a first prepared surface and a secondprepared surface. The method further comprises providing a chemicalderivatization compound containing active functional groups that promoteadhesion. The method further comprises depositing the chemicalderivatization compound on each of the first and second preparedsurfaces to form a first functional group-adhesive promoter derivatizedlayer and a second functional group-adhesive promoter derivatized layer.The method further comprises applying an adhesive layer to at least oneof the derivatized layer of the first and second functionalgroup-adhesive promoter derivatized layer. The method further comprisesjoining the first and second structures together with the adhesive layerand the first and second functional group-adhesive promoter derivatizedlayer therebetween. The method further comprises heat curing theadhesive to the joined first and second structures to form a structuralbond between the first and second structures.

In another embodiment of the disclosure, there is provided a method forstructural bonding of polymeric composite structures of an aircraft. Themethod comprises providing a first polymeric composite aircraftstructure and a second polymeric composite aircraft structure. Themethod further comprises preparing a surface to be bonded on each of thefirst and second polymeric composite aircraft structures to form a firstprepared surface and a second prepared surface. The method furthercomprises providing a chemical derivatization compound containing activefunctional groups that promote adhesion. The method further comprisesdepositing the chemical derivatization compound on each of the first andsecond prepared surfaces to form a first functional group-adhesivepromoter derivatized layer and a second functional group-adhesivepromoter derivatized layer. The method further comprises applying anadhesive layer to at least one of the first and second functionalgroup-adhesive promoter derivatized layers. The method further comprisesjoining the first and second polymeric composite aircraft structurestogether with the adhesive layer and the first and second functionalgroup-adhesive promoter derivatized layers therebetween. The methodfurther comprises heat curing the adhesive layer to the joined first andsecond polymeric composite aircraft structures to form a structural bondbetween the first and second polymeric composite aircraft structures.

In another embodiment of the disclosure, there is provided a method ofapplying a high temperature hybridized molecular functional groupadhesion barrier coating to a surface of a structure. The methodcomprises providing a structure having at least one surface to bebonded. The method further comprises preparing the at least one surfaceto expose active reactive surface sites. The method further comprisesproviding one or more liquid or solid phase chemical derivatizationcompounds. The method further comprises applying heat to the one or moreliquid or solid phase chemical derivatization compounds to vaporize theone or more liquid or solid phase chemical derivatization compounds. Themethod further comprises depositing the one or more vaporized chemicalderivatization compounds on the prepared surface to form a derivatizedcomposite surface having hybridized molecular functional groups. Themethod further comprises heat curing the derivatized composite surfaceto form a high temperature hybridized molecular functional groupadhesion barrier coating.

In another embodiment of the disclosure, there is provided a method ofapplying a high temperature hybridized molecular functional groupadhesion barrier coating to a surface of a composite structure. Themethod comprises preparing a composite surface of a composite structureto expose active reactive surface sites. The method further comprisespositioning the composite structure in a derivatization chamber. Themethod further comprises positioning one or more liquid or solid phasechemical derivatization compounds in the derivatization chamber. Themethod further comprises sealing the derivatization chamber. The methodfurther comprises applying heat to the one or more liquid or solid phasechemical derivatization compounds to vaporize the one or more liquid orsolid phase chemical derivatization compounds. The method furthercomprises flowing the one or more vaporized chemical derivatizationcompounds over the prepared composite surface. The method furthercomprises depositing the one or more vaporized chemical derivatizationcompounds on the prepared composite surface to form a derivatizedcomposite surface having hybridized molecular functional groups. Themethod further comprises heat curing at an effective curing heattemperature for an effective curing heat time the derivatized compositesurface to form a high temperature hybridized molecular functional groupadhesion barrier coating. The method further comprises cooling thederivatized composite surface with the formed high temperaturehybridized molecular functional group barrier coating.

In another embodiment of the disclosure, there is provided a hightemperature hybridized molecular functional group adhesion barriercoating for a composite structure. The coating comprises one or morehybridized molecular functional groups attached to a composite surfaceof a composite structure, wherein the one or more hybridized molecularfunctional groups are hybridized through a chemical derivatizationprocess. The coating further comprises one or more chemicalderivatization compounds attached to the one or more hybridizedmolecular functional groups via a condensation reaction. The coating ispreferably resistant to high heat temperatures in a range of from about350 degrees Fahrenheit to about 2000 degrees Fahrenheit, and the coatingis preferably a thermally protective, toughened adhesion coating thatmitigates effects of a hostile operating environment.

The features, functions, and advantages that have been discussed can beachieved independently in various embodiments of the disclosure or maybe combined in yet other embodiments further details of which can beseen with reference to the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure can be better understood with reference to the followingdetailed description taken in conjunction with the accompanying drawingswhich illustrate preferred and exemplary embodiments, but which are notnecessarily drawn to scale, wherein:

FIG. 1 is an illustration of a perspective view of an exemplary aircraftfor which embodiments of the methods and structures made with themethods may be used;

FIG. 2A is an illustration of a partial cross-sectional exploded view ofan embodiment of a bonded structure made with one of the embodiments ofthe methods disclosed herein;

FIG. 2B is an illustration of a partial cross-sectional view of thebonded structure of FIG. 2A;

FIG. 2C is an illustration of a partial cross-sectional exploded view ofanother embodiment of a bonded structure made with one of theembodiments of the methods disclosed herein;

FIG. 2D is an illustration of a partial cross-sectional view of thebonded structure of FIG. 2C;

FIG. 2E is an illustration of a partial cross-sectional exploded view ofa bonded aircraft structure that may be made with one of the embodimentsof the methods disclosed herein;

FIG. 2F is an illustration of a partial cross-sectional view of thebonded aircraft structure of FIG. 2E;

FIG. 3A is an illustration of a partial cross-sectional exploded view ofan embodiment of a repair bonded structure made with one of theembodiments of the methods disclosed herein;

FIG. 3B is an illustration of a partial cross-sectional view of therepair bonded structure of FIG. 3A;

FIG. 4A is an illustration of the chemical structure of a bismaleimideprepolymer and its functional groups;

FIG. 4B is an illustration of the chemical structure of a first R groupfor the bismaleimide prepolymer of FIG. 4A;

FIG. 4C is an illustration of the chemical structure of a second R groupfor the bismaleimide prepolymer of FIG. 4A;

FIG. 4D is an illustration of a table listing the functional groups ofthe bismaleimide prepolymer of FIG. 3A and the reactions of thefunctional groups;

FIG. 5 is an illustration of a bromination derivatization reactionmechanism of the functional groups of the bismaleimide prepolymer beforeand after the bromination reaction;

FIG. 6A is an illustration of the chemical structure of a chemicalderivatization compound pentafluorophenol that may be used inembodiments of the methods disclosed herein;

FIG. 6B is an illustration of the chemical structure of a chemicalderivatization compound allyl pentafluorobenzene that may be used inembodiments of the methods disclosed herein;

FIG. 6C is an illustration of the chemical structure of a chemicalderivatization compound tridecafluorononyl maleimide that may be used inembodiments of the methods disclosed herein;

FIG. 6D is an illustration of the chemical structure of a chemicalderivatization compound glycidyloctafluoropentyl ether that may be usedin embodiments of the methods disclosed herein;

FIG. 7 is an illustration of a silination derivatization reactionmechanism that may be used in embodiments of the methods disclosedherein;

FIG. 8 is an illustration of a thionation derivatization reactionmechanism that may be used in embodiments of the methods disclosedherein;

FIG. 9 is an illustration of a table listing the potential bismaleimideadhesion reactions;

FIG. 10 is an illustration of a graph comparing bismaleimide surfacecompositions after various surface preparation treatments;

FIG. 11 is an illustration of a graph comparing bismaleimide surfacecompositions before and after tetrafluoroaceticanhydride (TFAA)exposure;

FIG. 12 is an illustration of a graph comparing derivatized bismaleimidesurface compositions after exposure to various fluorinated chemicalderivatization compounds;

FIG. 13 is an illustration of a graph comparing the results of bromineand tetrafluoroaceticanhydride (TFAA) derivatization on shear strengthof bismaleimide-adhesive joints;

FIG. 14 is an illustration of a graph showing the results of the bindingenergy of fluorine of pentafluorophenol to resin and fibers of aderivatized bismaleimide surface;

FIG. 15 is an illustration of a graph showing the results of the bindingenergy of fluorine of allyl pentafluorobenzene to resin and fibers of aderivatized bismaleimide surface;

FIG. 16 is an illustration of a graph showing the results of the bindingenergy of fluorine of tridecafluorononyl maleimide to resin and fibersof a derivatized bismaleimide surface;

FIG. 17 is an illustration of a graph showing the results of the bindingenergy of fluorine of glycidyloctafluoropentyl ether to resin and fibersof a derivatized bismaleimide surface;

FIG. 18 is an illustration of a flow diagram of one of the embodimentsof a method of the disclosure;

FIG. 19 is an illustration of a flow diagram of another one of theembodiments of a method of the disclosure;

FIG. 20 is an illustration of a flow diagram of another one of theembodiments of a method of the disclosure;

FIG. 21 is an illustration of a partial cross-sectional view of anexemplary chemical vapor deposition in a vacuum bag set-up that may beused with embodiments of the methods of the disclosure;

FIG. 22 is an illustration of a BMI derivatization reaction mechanismthat may be combined with an epoxy derivatization reaction mechanism ofFIG. 23 and used in embodiments of the methods disclosed herein;

FIG. 23 is an illustration of an epoxy derivatization reaction mechanismthat may be combined with a BMI derivatization reaction mechanism ofFIG. 22 and that may be used in embodiments of the methods disclosedherein;

FIG. 24 is an illustration of a table listing atomic compositions ofmodel chemical derivatization compounds deposited on a BMI surface;

FIG. 25 is an illustration of a table listing atomic compositions ofelements of model chemical derivatization compounds deposited on anepoxy derivatized surface and on a BMI derivatized surface;

FIG. 26 is an illustration of a table listing the effect ofderivatization on surface energy for various derivatizing agents;

FIG. 27 is an illustration of a table listing surface characterizationfor surface energy of epoxy and BMI control and derivatized surfaces;

FIG. 28 is an illustration of a table listing reactive surface sites onBMI for various derivatizing agents;

FIG. 29 is an illustration of a graph showing adhesive fracturetoughness results for bonded to functionalized surfaces;

FIG. 30 is an illustration of a partial cross-sectional view of anotherexemplary chemical vapor deposition in a vacuum bag set-up that may beused with embodiments of the methods of the disclosure; and,

FIG. 31 is an illustration of a flow diagram of another one of theembodiments of a method of the disclosure.

DETAILED DESCRIPTION

Disclosed embodiments will now be described more fully hereinafter withreference to the accompanying drawings, in which some, but not all ofthe disclosed embodiments are shown. Indeed, several differentembodiments may be provided and should not be construed as limited tothe embodiments set forth herein. Rather, these embodiments are providedso that this disclosure will be thorough and complete and will fullyconvey the scope of the disclosure to those skilled in the art.

Now referring to the Figures, FIG. 1 is an illustration of a perspectiveview of an exemplary prior art aircraft 10 for which embodiments ofmethods 150 (see FIG. 18), 200 (see FIG. 19), 300 (see FIG. 20), andstructurally bonded structures 30 (see FIGS. 2A, 2B), 50 (see FIGS. 2C,2D), and 170 (see FIGS. 2E, 2F), and repair bonded structure 60 (seeFIGS. 3A, 3B) made from such methods 150, 200, 300, may be used. Asshown in FIG. 1, the aircraft 10 comprises a fuselage 12, a nose 14, acockpit 16, wings 18 operatively coupled to the fuselage 12, one or morepropulsion units 20, a tail vertical stabilizer 22, and one or more tailhorizontal stabilizers 24. Although the aircraft 10 shown in FIG. 1 isgenerally representative of a commercial passenger aircraft, the methods150, 200, 300, and structurally bonded structures 30 (see FIGS. 2A, 2B),50 (see FIGS. 2C, 2D), and repair bonded structure 60 (see FIGS. 3A, 3B)made from such methods 150, 200, 300, as disclosed herein, may also beemployed in other types of aircraft. More specifically, the teachings ofthe disclosed embodiments may be applied to other passenger aircraft,cargo aircraft, military aircraft, rotorcraft, and other types ofaircraft or aerial vehicles, as well as aerospace vehicles, satellites,space launch vehicles, rockets, and other aerospace vehicles. It mayalso be appreciated that embodiments of methods, systems, andapparatuses in accordance with the disclosure may be utilized in othervehicles, such as boats and other watercraft, trains, automobiles,trucks, and buses, as well as buildings and other architecturalstructures that use composite, ceramic and metal structural components.

In one of the embodiments there is provided a bonded structure 30 (seeFIGS. 2A, 2B) that may be formed or made with embodiments of the methods150, 200, 300 disclosed herein. FIG. 2A is an illustration of a partialcross-sectional exploded view of an exemplary embodiment of a bondedstructure 30 that may be made with embodiments of the methods 150, 200,300 disclosed herein. FIG. 2B is an illustration of a partialcross-sectional view of the bonded structure 30 of FIG. 2A. Preferably,the bonded structure 30 is a composite bonded structure comprising afirst composite structure or substrate 32 having a first compositesurface 34 to be bonded and a second composite structure or substrate 36having a second composite surface 38 to be bonded. As discussed indetail below, the first composite surface 34 and/or the second compositesurface 38 are prepared or treated with a surface preparation treatmentor process prior to structural bonding. The first and second compositestructures 32, 36 are made of a polymeric composite material comprisingpreferably, one or more of bismaleimides (BMI), epoxies, or anothersuitable polymeric composite material; more preferably, graphite(Gr)/bismaleimide, graphite (Gr)/epoxy, or graphite (Gr)/polyimide; andmost preferably, graphite (Gr)/bismaleimide (BMI).

In another one of the embodiments there is provided a bonded structure50 (see FIGS. 2C, 2D) that may be formed or made with embodiments of themethods 150, 200, 300 disclosed herein. FIG. 2C is an illustration of apartial cross-sectional exploded view of the bonded structure 50 thatmay be made with one of the embodiments of the methods 150, 200, 300disclosed herein. FIG. 2D is an illustration of a partialcross-sectional view of the bonded structure 50 of FIG. 2C. The bondedstructure 50 may comprise the first composite structure or substrate 32having the first composite surface 34 to be bonded and may comprise ametal structure or substrate 52 having a metal surface 54 to be bonded.The metal structure or substrate 52 may preferably be made of a metalmaterial, such as aluminum, titanium, steel, alloys thereof, or anothersuitable metal material. As discussed in detail below, the firstcomposite surface 34 and/or the second metal surface 34 are prepared ortreated with a surface preparation treatment or process prior tostructural bonding. Alternatively, the bonded structure may comprise afirst metal structure or substrate bonded to a second metal structure orsubstrate without a primer layer.

In another one of the embodiments there is provided a bonded polymericcomposite aircraft structure 170 (see FIGS. 2E, 2F) for an aircraft 10(see FIGS. 1, 2E, 2F) that may be formed or made with embodiments of themethods 150, 200, 300 disclosed herein. FIG. 2E is an illustration of apartial cross-sectional exploded view of the bonded aircraft structure170 that may be made with one of the embodiments of the methods 150,200, 300 disclosed herein. FIG. 2F is an illustration of a partialcross-sectional view of the bonded aircraft structure 170 of FIG. 2E.The bonded polymeric composite aircraft structure 170 may comprise afirst polymeric composite aircraft structure 172 and a second polymericcomposite aircraft structure 176 in an aircraft 10. Preferably, thebonded aircraft structure has a first prepared surface 174 and a secondprepared surface 178 that has been prepared or treated with a surfacepreparation treatment or process, discussed in detail below, prior tostructural bonding. The first and second polymeric composite aircraftstructures 172, 176 are made of a polymeric composite materialcomprising preferably, one or more of bismaleimides (BMI), epoxies,polyimides, or another suitable polymeric composite material; morepreferably, graphite (Gr)/bismaleimide, graphite (Gr)/epoxy, or graphite(Gr)/polyimide; and most preferably, graphite (Gr)/bismaleimide (BMI).

In another one of the embodiments there is provided a repair bondedstructure 60 that may be formed or made with embodiments of the methods150, 200, 300 is disclosed. FIG. 3A is an illustration of a partialcross-sectional exploded view of an embodiment of the repair bondedstructure 60 that may be made with embodiments of the methods 150, 200,300 disclosed herein. FIG. 3B is an illustration of a partialcross-sectional view of the repair bonded structure 60 of FIG. 3A. Asshown in FIGS. 3A and 3B, the repair bonded structure 60 is preferably acomposite structure comprising a first composite structural portion 62having a first composite surface 64 to be repair bonded and a secondcomposite structural portion 66 having a second composite surface 68 tobe repaired. The first and second composite structural portions 62, 66may be made of a polymeric composite material comprising preferably, oneor more of bismaleimides (BMI), epoxies, polyimides, or another suitablepolymeric composite material; more preferably, graphite(Gr)/bismaleimide, graphite (Gr)/epoxy, or graphite (Gr)/polyimide; andmost preferably, bismaleimide (BMI). As discussed in detail below, thefirst composite surface 64 and/or the second composite surface 68 areprepared or treated with a surface preparation treatment or processprior to repair bonding.

As further shown in FIGS. 2A-2F and 3A, 3B, the bonded structures 30,50, 170 and the repair bonded structure 60 further comprise at least onefunctional group-adhesive promoter derivatized layer 40 that isdeposited on the prepared composite or metal surface to be bonded. Thefunctional group-adhesive promoter derivatized layer 40 has a surface 42and functional groups 44 which are discussed in detail below. As shownin FIGS. 2A, 2C, 2E, 3A, the bonded structures 30, 50, 170 and therepair bonded structure 60 may comprise a first functionalgroup-adhesive promoter derivatized layer 40 a and a second functionalgroup-adhesive promoter derivatized layer 40 b. As shown in FIGS. 2A-2Fand 3A, 3B, the bonded structures 30, 50, 170 and the repair bondedstructure 60 each further comprise an adhesive layer 46, discussed indetail below, that is applied to the surface 42 of at least one of thefunctional group-adhesive promoter derivatized layers 40, so as to forma structural bond 48 (see FIG. 2B), structural bond 56 (see FIG. 2D), anaircraft structural bond 180 (see FIG. 2F), or a repair bond 70 (seeFIG. 3B).

In another one of the embodiments of the disclosure, there is provided amethod 150, as shown in FIG. 18, of promoting adhesion on a compositesurface prior to bonding, such as structural bonding or repair bonding.FIG. 18 is an illustration of a flow diagram of one of the embodimentsof the method 150 of the disclosure. The method 150 comprises step 152of providing a composite structure or substrate 32 (see FIGS. 2A-2B)having at least one composite surface 34 (see FIGS. 2A-2B) to be bondedor repaired. The composite structure or substrate 32 is made of apolymeric composite material comprising preferably, one or more ofbismaleimides (BMI), epoxies, polyimides, or another suitable polymericcomposite material; more preferably, graphite (Gr)/bismaleimide,graphite (Gr)/epoxy, or graphite (Gr)/polyimide; and most preferably,graphite (Gr)/bismaleimide (BMI). Bismaleimides are particularlypreferred for use in high performance structural composites requiringhigher temperature use and increased toughness and durability. Thedouble bond of the maleimide is very reactive and can undergo chainextension reactions. Epoxy blends of bismaleimide have exhibited usetemperatures of 205° C. (degrees Celsius) to 245° C. and increasedtoughness and durability.

FIG. 4A is an illustration of the chemical structure of a bismaleimideprepolymer 72 and shows the functional groups of allyl 74 and hydroxyl76 and “R” group 78. FIG. 4B is an illustration of the chemicalstructure where the “R” group 78 is propenyl 80 for the bismaleimideprepolymer 72 of FIG. 4A. FIG. 4C is an illustration of the chemicalstructure where the “R” group 78 is maleimide 82 for the bismaleimideprepolymer 72 of FIG. 4A. FIG. 4D is an illustration of a table 84listing the functional groups allyl 74, hydroxyl 76, propenyl 80, andmaleimide 82 of the bismaleimide prepolymer 72 of FIG. 3A and thereactions of the functional groups. As shown in the table 84 of FIG. 4D,the reaction of allyl 74 is an addition reaction to maleimide, thereaction of hydroxyl 76 is a condensation reaction to ether, and thereactions of propenyl 80 and maleimide 82 are crosslinking viahomopolymerization. For purpose of this disclosure, “functional groups”mean specific groups of atoms within molecules that are responsible forthe characteristic chemical reactions of those molecules. The atoms offunctional groups are linked to each other and to the rest of themolecule by covalent bonds. Organic reactions are facilitated andcontrolled by the functional groups of the reactants.

The method 150 further comprises step 154 of preparing or treating withone or more surface preparation treatments the at least one compositesurface 34 (see FIGS. 2A, 2C) prior to structural bonding or compositesurface 64 (see FIG. 3A) prior to repair bonding. In addition, thepreparing or treating step 154 with one or more surface preparationtreatments may comprise preparing or treating composite surface 38 (seeFIG. 2A) or metal surface 54 (see FIG. 2C) prior to structural bondingor composite surface 68 (see FIG. 3A) prior to repair bonding Thecomposite, metal or combination composite/metal surfaces may be preparedwith one or more surface preparation treatments comprising solventwiping, abrading, grit blasting, sanding, sandblasting, chemicalcleaning, chemical etching, or another suitable surface preparationtreatment.

In particular, structural bonding processes rely on sanding to removecontaminants, and increase the surface energy on a limited basis on thecomposite surface. Preparing or treating the composite surface, such assanding the composite surface, unexpectedly exposed unique andadditional secondary functional groups on the composite surface thathave positive durable adhesive promoter effects by increasing adhesivewettability tension and long-term bonding joint durability betweencomposite structures, for example, an aircraft skin and an aircraftstringer. Increased surface energy due to these unique and additionalsecondary functional groups improves the wettability tension of theadhesive that results in mechanical lock between composite structures.For purposes of this disclosure, “wettability tension” means the abilityof a solid surface to reduce the surface tension of a liquid in contactwith it such that it spreads over the surface and wets it. Fluids withlow surface tension have high wettability, and fluids with high surfacetension have low wettability.

The method 150 further comprises step 156 of providing a chemicalderivatization compound, such as for example, a fluorinated compound,tetrafluoroaceticanhydride (TFAA), pentafluorophenol, allylpentafluorobenzene, tridecafluorononyl maleimide,glycidyloctafluoropentyl ether, or another fluorinated compound oranother suitable chemical derivatization compound. FIG. 6A is anillustration of the chemical structure of chemical derivatizationcompound pentafluorophenol 90 that may be used in method 150, as well asmethods 200, 300 disclosed herein. FIG. 6B is an illustration of thechemical structure of chemical derivatization compound allylpentafluorobenzene 92 that may be used in method 150, as well as methods200, 300 disclosed herein. FIG. 6C is an illustration of the chemicalstructure of chemical derivatization compound tridecafluorononylmaleimide 94 that may be used in method 150, as well as methods 200, 300disclosed herein. FIG. 6D is an illustration of the chemical structureof chemical derivatization compound glycidyloctafluoropentyl ether 96that may be used in method 150, as well as methods 200, 300 disclosedherein. The chemical derivatization compounds contain active functionalgroups that promote adhesion and detect adhesion mechanisms. Forexample, as shown in FIGS. 6A-6D, pentafluorophenol 90 containshydroxyl, allyl pentafluorobenzene 92 contains allyl, tridecafluorononylmaleimide 94 contains maleimide, and glycidyloctafluoropentyl ether 96contains epoxy.

The method 150 further comprises step 158 of depositing or applying thechemical derivatization compound on the composite surface 34 or 64, forexample, that has been prepared in order to form a functionalgroup-adhesive promoter derivatized layer 40 (see FIGS. 2A-2D and 3A-3B)via a derivatization reaction. For purposes of this disclosure, the term“derivatization” means a technique or reaction used in chemistry whichtransforms a chemical compound into a product (a reaction's derivate) ofsimilar chemical structure called a derivative. A specific functionalgroup of the compound participates in the derivatization reaction andtransforms the educt to a derivate of deviating reactivity, solubility,boiling point, melting point, aggregate state, or chemical composition.The derivatization reactions used in the methods 150, 200, 300 disclosedherein transform the composite surface 34 or 64, for example, bycovalently bonding chemicals or molecules to the composite surface 34 or64.

The chemical derivatization compound 90, 92, 94, 96, may be deposited onthe prepared composite surface 34 or 64, for example, via chemical vapordeposition, such as chemical vapor deposition in a vacuum bag set-up,vacuum deposition, or another suitable deposition or applicationprocess. FIG. 21 is an illustration of a partial cross-sectional view ofan exemplary chemical vapor deposition in a vacuum bag set-up 250 thatmay be used with embodiments of the methods 150, 200, 300 of thedisclosure. As shown in FIG. 21, the chemical vapor deposition in avacuum bag set-up 250 comprises a vacuum bag 256 coupled with seals 258to a top surface 252 of a flat table 254 or other flat surface. Aseparator element 260, such as for example, a mesh wire screen, may beplaced between the vacuum bag 256 and the first composite structure orsubstrate 32. A liquid or solid phase chemical derivatization compound264 is poured into a container 262, such as a glass vial, and is heatedwith a heat source 266. With heat, the liquid or solid phase chemicalderivatization compound 264 vaporizes to become a vapor phase orvaporized chemical derivatization compound 268. The vapor phase chemicalderivatization compound 268 travels along a path 270 and over thesubstrate 32 to react and deposit to form the functional group-adhesivepromoter derivatized layer 40 on the substrate 32. Any vapor phasechemical derivatization compound 268 that is unreacted travels along thepath 270 and through a vacuum port 272 and an opening 274 in the vacuumbag 256. The vacuum port 272 comprises a first portion 276 attachedabove the vacuum bag 256 and a second portion 278 attached below thevacuum bag 256. Any unreacted vapor phase chemical derivatizationcompound 280 escapes out of the vacuum port 272 and out of the vacuumbag set-up 250. Preferably, the prepared composite surface or substrate34 or 64, for example, may be exposed to the vapor phase chemicalderivatization compound 268 containing selected functional groups. Theselection of the functional groups is preferably based on a resinformulation of the composite structure, for example. In particular, forcomposite structures made of bismaleimide, it has been unexpectedlyfound that the chemical derivatization compounds 90, 92, 94, 96 formcarbon-carbon double bond functional groups on a derivatized surface ofthe bismaleimide.

Derivatization reaction mechanisms capable of creating reactive usefulfunctional groups on a composite structure include such derivatizationreaction mechanisms as bromination, silination, and thionation. FIG. 5is an illustration of a bromination derivatization reaction mechanism 86in which the functional groups allyl 74, propenyl 80, and maleimide 82of the bismaleimide prepolymer 72 (see FIG. 4A) react with bromine 88 toobtain a bromination reaction product 89. The bromination derivatizationreaction attacks double bonds exposed on the composite surface. Doublebonds are electron rich environments that promote secondary bondingforces between the adhesive and the composite structural surface.

FIG. 7 is an illustration of a silination derivatization reactionmechanism 98 in which a silane solution or gel 100 reacts withcarbon-carbon double bond 102 to obtain a silination reaction product104. The silination derivatization reaction is capable of reaction withunits of unsaturation on the composite surface and introduces entireorganic functional groups onto the composite surface.

FIG. 8 is an illustration of a thionation derivatization reactionmechanism 106 in which a thiol solution or gel 108 reacts withcarbon-carbon double bond 102 to obtain a thionation reaction product110. The thionation derivatization reaction reacts with units ofunsaturation introducing organic containing sulfur functional groupsonto the composite surface.

X-ray photoelectron spectroscopy techniques can be used to identifyspecific functional groups that influence a composite to composite bondor joint when one or both composites are made from a bismaleimide matrixmaterial. FIG. 9 is an illustration of a table 112 listing the potentialbismaleimide adhesion reactions, including the functional group types,the possible reactions with bismaleimide/epoxy adhesive, and thetemperature range. For the functional group allyl 74, the possiblereaction with bismaleimide/epoxy adhesive is “ene” addition to maleimideat a temperature in the range of 200° C. (degrees Celsius) to 300° C.For the functional group hydroxyl 76, the possible reaction withbismaleimide/epoxy adhesive is etherification at a temperature ofgreater than 240° C. For the functional group hydroxyl-epoxide, thepossible reaction with bismaleimide/epoxy adhesive is epoxy addition ata temperature of greater than 100° C. For the functional group maleimide82, the possible reaction with bismaleimide/epoxy adhesive is maleimideaddition to maleimide at a temperature of greater than 100° C.

The method 150, as well as methods 200, 300, discussed below, introduceunique functional groups as a structural adhesive promoter on compositesurfaces made of a polymeric composite material comprising preferably,one or more of bismaleimides (BMI), epoxies, polyimides, or anothersuitable polymeric composite material; more preferably, graphite(Gr)/bismaleimide, graphite (Gr)/epoxy, or graphite (Gr)/polyimide; andmost preferably, bismaleimide (BMI). This is achieved by introducingfunctional groups though derivatization reaction mechanisms on thecomposite surface to be bonded such as for structural bonding or repairbonding. These functional groups accelerate the secondary interactionbetween the adhesive and the composite surface thereby increasing therepair design long life and durability of the composite bonded jointunder hostile operating environments. The method 150, as well as methods200, 300, discussed below, transform the composite surface of thecomposite structure from a limited active surface to a highly activatedadhesive promoter of durable-bonding surface characteristics. A varietyof forces are presumed to be responsible for a successful and effectivecomposite bonded joint or repair bond. Primary bonding forces includethe covalent bonds created between the composite surface and theadhesive material, as well as Van der Waals forces that are also createdat the composite-adhesive interface. For purposes of this disclosure,“Van der Waals forces” mean the sum of the attractive or repulsiveforces between molecules or between parts of the same molecule otherthan those due to covalent bonds or to electrostatic interaction of ionswith one another or with neutral molecules. For purposes of thisdisclosure, “covalent bonds” means a chemical bond that is characterizedby the sharing of pairs of electrons between atoms, and other covalentbonds.

The method 150, as well as methods 200, 300, discussed below, usechemical derivatization to create a functional group-adhesive promotertype layer on the structural composite surface as a bonding agent.Morever, on bismaleimide composite surfaces, the formation ofcarbon-carbon double bond (C═C) (unsaturation) functional groups on suchsurfaces through derivatization reactions was unexpectedly found, whichresults in a structurally sound and durable composite bond that can beused in various structures, for example, aircraft structures. A monolayer of derivatizing chemicals at otherwise inactive sites on thecomposite surface creates a thin film adhesive promoter that promotesadhesion. For purposes of this disclosure, “adhesive promoter” means amaterial that helps an adhesive bond to a surface and that is applied tothe surface before the adhesive is applied.

The method 150 further comprises step 160 of applying an adhesive layer46 (see FIGS. 2A-2F and 3A, 3B) to the surface 42 of the functionalgroup-adhesive promoter derivatized layer 40 of at least, for example,the composite structure 32 (see FIGS. 2A, 2C), the first polymericcomposite aircraft structure 172 (see FIG. 2E), or the first compositestructural portion 62 (see FIG. 3A). In addition, the adhesive layer 46may also be applied to the surface 42 of the functional group-adhesivepromoter derivatized layer 40 of the composite structure 36 (see FIG.2A) or the second polymeric composite aircraft structure 176 (see FIG.2E) or the metal structure 52 (see FIG. 2C) or the second compositestructural portion 66 (see FIG. 3A). The adhesive layer 46 maypreferably comprise film adhesives, such as epoxies, bismaleimides, oranother suitable adhesive.

The method 150 further comprises step 162 of heat curing the adhesivelayer 46 to result in a bond with another structure made of a composite,a metal, or a combination thereof. The bond may comprise, for example, astructural bond 48 (see FIG. 2B), 56 (see FIG. 2D), or 180 (see FIG.2F), or a repair bond 70 (see FIG. 3B). As shown in the drawings, heatcuring the adhesive layer 46 can result in the structural bond 48 (seeFIG. 2B) with another structure, such as between first compositestructure 32 and second composite structure, or can result in thestructural bond 56 (see FIG. 2D) with another structure, such as betweenfirst composite structure 32 and metal structure 52, or can result inthe aircraft structural bond 180 (see FIG. 2F) with another structure,such as between first polymeric composite aircraft 172 and secondpolymeric composite aircraft structure 174, or can result in the repairbond 70 (see FIG. 3B), such as between first composite structuralportion 62 and second composite structural portion 66. The otherstructure may comprise, for example, a composite structure 36 (see FIGS.2A-2B) that is comprised of the same composite material as the compositestructure 32 or a different composite material than the compositestructure 32. In another embodiment, the other structure may comprise ametal structure 52 (see FIGS. 2C-2D) that may preferably be made of ametal material such as aluminum, titanium, steel, alloys thereof, oranother suitable metal material. In another embodiment, the otherstructure may comprise a structure made of a combination of a compositematerial and a metal material. The composite structure 32 and the otherstructure made of the composite, the metal, or the combination thereof,are preferably aircraft structures for manufacturing an aircraft 10 (seeFIG. 1), for example, polymeric aircraft structures 172, 176 (see FIG.2E) may be used to form the wings 18 or fuselage 12 or aircraft 10.

FIG. 19 is an illustration of a flow diagram of another one of theembodiments of a method 200 for structural bonding of structures. Themethod 200 comprises step 202 of providing a first structure 32 (seeFIGS. 2A-2D) made of a composite material and a second structure 36 (seeFIG. 2A) made of a composite material, a second structure 52 made of ametal material, or a second structure made of a combination of acomposite material and a metal material. The first composite structure32 and the second structure, if made of a composite material or acombination of composite material, are made of a polymeric compositematerial comprising preferably, one or more of bismaleimides (BMI),epoxies, polyimides, or another suitable polymeric composite material;more preferably, graphite (Gr)/bismaleimide, graphite (Gr)/epoxy, orgraphite (Gr)/polyimide; and most preferably, bismaleimide (BMI). If thesecond structure is made of metal material or a combination of metalmaterial and composite material, preferably the metal material comprisesuch as aluminum, titanium, steel, alloys thereof, or another suitablemetal material. Preferably, the first and second structures are aircraftstructures.

The method 200 further comprises step 204 of preparing a surface to bebonded, such as composite surfaces 34, 38 (see FIG. 2A) or a metalsurface 54 (see FIG. 2C) on each of the first and second structures 32,36 (see FIG. 2A) or 32, 52 (see FIG. 2C) to obtain a first surface 34that has been prepared and a second surface 38 or 54 that has beenprepared. As discussed above, the surface to be bonded is preferablyprepared with one or more surface preparation treatments comprisingsolvent wiping, abrading, grit blasting, sanding, sandblasting, chemicaletching, or another suitable surface preparation treatment.

The method 200 further comprises step 206 of providing a chemicalderivatization compound (90, 92, 94, 96 (see FIGS. 6A-6D)) containingactive functional groups that promote adhesion. As discussed above, thechemical derivatization compound preferably comprises fluorinatedcompounds, tetrafluoroaceticanhydride (TFAA), pentafluorophenol, allylpentafluorobenzene, tridecafluorononyl maleimide,glycidyloctafluoropentyl ether, or another fluorinated compound, oranother suitable chemical derivatization compound. The method 200further comprises step 208 of depositing the chemical derivatizationcompound (90, 92, 94, 96 (see FIGS. 6A-6D)) on each of the first andsecond surfaces 34, 38 (see FIG. 2A) or 34, 54 (see FIG. 2C) that havebeen prepared in order to form a first functional group-adhesivepromoter derivatized layer 40 a (see FIGS. 2A, 2C) and a secondfunctional group-adhesive promoter derivatized layer 40 b (see FIGS. 2A,2C). The chemical derivatization compound may be deposited on theprepared composite surface via chemical vapor deposition, such aschemical vapor deposition in a vacuum bag set-up; vacuum deposition; oranother suitable deposition or application process. The chemical vapordeposition in a vacuum bag set-up 250 is shown in FIG. 21 and isdiscussed in detail above. The method 200 further comprises step 210 ofapplying an adhesive layer 46 to at least one of the first and secondfunctional group-adhesive promoter derivatized layers 40 a, 40 b. Asdiscussed above, the adhesive layer 46 may preferably comprise filmadhesives, such as epoxies, bismaleimides, or another suitable adhesive.

The method 200 further comprises step 212 of joining the first andsecond structures 32, 36 (see FIG. 2A) or 32, 52 (see FIG. 2C) togetherwith the adhesive layer 46 and the first and second functionalgroup-adhesive promoter derivatized layers 40 a, 40 b therebetween. Themethod 200 further comprises step 214 of heat curing the adhesive layer46 to the joined first and second structures 32, 36 (see FIG. 2A) or 32,52 (see FIG. 2C) to form a structural bond 48 (see FIG. 2B) or 56 (FIG.2D) between the first and second structures 32, 36 (see FIG. 2A) or 32,52 (see FIG. 2C), respectively. The first structure 32 made of acomposite material is preferably an aircraft structure. The other secondstructure 36 (see FIG. 2A) made of the composite, the other secondstructure 52 made of the metal, or the other second structure made of acombination of composite and metal, are also preferably aircraftstructures.

FIG. 20 is an illustration of a flow diagram of another one of theembodiments of a method 300 for structural bonding of polymericcomposite structures of an aircraft 10 (see FIGS. 1, 2E, 2F). The method300 comprises step 302 of providing a first polymeric composite aircraftstructure 172 and a second polymeric composite aircraft structure 176(see FIG. 2E). The first polymeric composite aircraft structure 172 andthe second polymeric composite aircraft structure 176 are made of apolymeric composite material comprising preferably, one or more ofbismaleimides (BMI), epoxies, polyimides, or another suitable polymericcomposite material; more preferably, graphite (Gr)/bismaleimide,graphite (Gr)/epoxy, or graphite (Gr)/polyimide; and most preferably,bismaleimide (BMI).

The method 300 further comprises step 304 of preparing a surface to bebonded on each of the first and second polymeric composite aircraftstructures 172, 176 in order to form a first prepared surface 174 and asecond prepared surface 178 (see FIG. 2E), respectively. The firstprepared surface 174 and the second prepared surface 178 are preferablyprepared with one or more surface preparation treatments comprisingsolvent wiping, abrading, grit blasting, sanding, sandblasting, chemicaletching, or another suitable surface preparation treatment.

The method 300 further comprises step 306 of providing a chemicalderivatization compound (90, 92, 94, 96 (see FIGS. 6A-6D)) containingactive functional groups that promote adhesion. As discussed above, thechemical derivatization compound preferably comprises fluorinatedcompounds, tetrafluoroaceticanhydride (TFAA), pentafluorophenol, allylpentafluorobenzene, tridecafluorononyl maleimide,glycidyloctafluoropentyl ether, or another fluorinated compound, oranother suitable chemical derivatization compound. The method 300further comprises step 308 of depositing the chemical derivatizationcompound (90, 92, 94, 96 (see FIGS. 6A-6D)) on each of the first andsecond prepared surfaces 174, 178, to form a first functionalgroup-adhesive promoter derivatized layer 40 a and a second functionalgroup-adhesive promoter derivatized layer 40 b (see FIG. 2E). Thechemical derivatization compound may be deposited on the first andsecond prepared surfaces 174, 178 via chemical vapor deposition, such aschemical vapor deposition in a vacuum bag set-up; vacuum deposition; oranother suitable deposition or application process. The chemical vapordeposition in a vacuum bag set-up 250 is shown in FIG. 21 and isdiscussed in detail above. For first and second polymeric compositeaircraft structures 172, 176 made of bismaleimide, chemicalderivatization compounds can form carbon-carbon double bond functionalgroups on the derivatized layer or surface of the bismaleimide.

The method 300 further comprises step 310 of applying an adhesive layer46 to at least one of the first and second functional group-adhesivepromoter derivatized layers 40 a, 40 b. As discussed above, the adhesivelayer 46 may preferably comprise film adhesives, such as epoxies,bismaleimides, or another suitable adhesive. The method 300 furthercomprises step 312 of joining the first and second polymeric compositeaircraft structures 172, 176 together with the adhesive layer 46 and thefirst and second functional group-adhesive promoter derivatized layers40 a, 40 b therebetween. The method 300 further comprises step 314 ofheat curing the adhesive layer 46 to the joined first and secondpolymeric composite aircraft structures 172, 176 to form an aircraftstructural bond 180 (see FIG. 2F) between the first and second polymericcomposite aircraft structures 172, 176.

In another embodiment of the disclosure, there is provided a method 500of applying a high temperature hybridized molecular functional groupadhesion barrier coating to a surface 454 (see FIG. 30) of a structure452 or substrate (see FIG. 30). FIG. 31 is an illustration of a flowdiagram of another one of the embodiments of the method 500 of thedisclosure. As shown in FIG. 31, the method 500 comprises step 502 ofproviding a structure 452 having at least one surface 454 to be bonded.The structure 452 or substrate may comprise a material such as acomposite material, a metal material, a ceramic material, or anothersuitable material. The composite material preferably comprisesbismaleimides (BMI), epoxies, polyimides, graphite/bismaleimide,graphite/epoxy, graphite/polyimide, a combination thereof, or anothersuitable composite material. The metal material preferably comprisessuper alloys such as nickel and copper based alloys, titanium, hightemperature refractory alloys, or another suitable metal material. Theceramic material preferably comprises refractory based high temperatureceramic structural materials or another suitable ceramic material. Thestructure is preferably an aircraft structure, and more preferably, anacelle, a fuel tank, an engine or another aircraft structure that maybe exposed to high temperatures.

The method 500 further comprises step 504 of preparing the at least onesurface 454 (see FIG. 30) to expose active reactive surface sites. Thesurface 454 may be prepared with one or more surface preparationtreatments such as hand sanding, machine sanding, sandblasting, solventwiping, abrading, grit blasting, chemical cleaning, chemical etching, oranother suitable surface preparation treatment. Preferably, the surfacepreparation treatment is hand sanding.

The surface 454 that has been prepared may then be preferably placedinto a treatment vessel or derivatization chamber, such as a vacuum bag256 in chemical vapor deposition vacuum bag set-up 450 (see FIG. 30).FIG. 30 is an illustration of a partial cross-sectional view of anexemplary chemical vapor deposition in a vacuum bag set-up 450 that maybe used with embodiments of the methods, such as method 500, of thedisclosure. As shown in FIG. 30, the chemical vapor deposition in avacuum bag set-up 450 comprises a vacuum bag 256 coupled with seals 258to a top surface 252 of a flat table 254 or other flat surface. Asfurther shown in FIG. 30, a separator element 260, such as for example,a mesh wire screen, may be placed between the vacuum bag 256 and astructure 452 or substrate having a surface 454.

The method 500 further comprises step 506 of providing one or moreliquid or solid phase chemical derivatization compounds. The one or moreliquid or solid phase chemical derivatization compounds may consist ofpentafluorophenol 90 (see FIG. 6A), allyl pentafluorobenzene (see FIG.6B), tridecafluorononyl maleimide (see FIG. 6C), glycidyloctafluoropentyl ether (see FIG. 6D), and fluorinated compounds.

The method 500 further comprises step 508 of applying heat to the one ormore liquid or solid phase chemical derivatization compounds to vaporizethe one or more liquid or solid chemical derivatization compounds. Theheat applied to the one or more liquid or solid phase chemicalderivatization compounds is preferably in a temperature range of fromabout 350 degrees Fahrenheit to about 500 degrees Fahrenheit. As shownin FIG. 30, a first liquid or solid phase chemical derivatizationcompound 264 a is placed into a first container 262 a, such as a glassvial, and is heated with a first heat source 226 a, and a second liquidor solid phase chemical derivatization compound 264 b is placed into asecond container 262 b, such as a glass vial, and is heated with asecond heat source 226 b.

The method 500 further comprises step 510 of depositing the one or morevaporized chemical derivatization compounds on the surface 454 that hasbeen prepared to form a derivatized surface 400 b (see FIG. 22) or 402 b(see FIG. 23) having hybridized molecular functional groups, such ashydroxyl 76 (see FIG. 4A), maleimide 82 (see FIG. 4C), allyl 74 (seeFIG. 74), and imide 83 (see FIG. 23). Preferably, the derivatizedsurface is a composite derivatized surface.

FIG. 22 is an illustration of a BMI derivatization reaction mechanismthat may be combined with an epoxy derivatization reaction mechanism ofFIG. 23 and used in embodiments of the methods, such as method 500,disclosed herein. FIG. 23 is an illustration of an epoxy derivatizationreaction mechanism that may be combined with a BMI derivatizationreaction mechanism of FIG. 22 and that may be used in embodiments of themethods, such as method 500, disclosed herein. The hybridized molecularfunctional groups preferably comprise hydroxyl 76 (see FIG. 4A),maleimide 82 (see FIG. 4C), allyl 74 (see FIG. 74), and imide 83 (seeFIG. 23). In particular, a cured surface 400 a for BMI (bismaleimide)(see FIG. 22) and a derivatized surface 400 b for BMI (see FIG. 22) havethe hybridized molecular functional groups of allyl 74, maleimide 82,and hydroxyl 76 (see FIG. 22), and a cured surface 402 a for epoxy (seeFIG. 23) and a derivatized surface 402 b for epoxy (see FIG. 23) havethe hybridized molecular functional groups of hydroxyl 76 and imide 83(see FIG. 23). The one or more vaporized chemical derivatizationcompounds may be deposited on the prepared surface via chemical vapordeposition, vacuum deposition, or another suitable deposition process.Preferably, the one or more chemical derivatization compounds may bedeposited on the prepared surface via chemical vapor deposition, such aschemical vapor deposition in a vacuum bag set-up 450.

As shown in FIG. 30, with heat, the first and second liquid or solidphase chemical derivatization compounds 264 a, 264 b vaporize to becomea first vaporized chemical derivatization compound 268 a and a secondvaporized chemical derivatization compound 268 b. The first and secondvaporized chemical derivatization compounds 268 a, 268 b travel alongrespective paths 270 a, 270 b and over the surface 454 of the substrate452 to react and deposit to form the derivatized surface havinghybridized molecular functional groups on the substrate 452. Any of thevaporized chemical derivatization compounds 268 a, 268 b that areunreacted travel along the respective paths 270 a, 270 b and through avacuum port 272 and an opening 274 in the vacuum bag 256. The vacuumport 272 comprises a first portion 276 attached above the vacuum bag 256and a second portion 278 attached below the vacuum bag 256. Unreactedvaporized chemical derivatization compounds 280 a, 280 b escape out ofthe vacuum port 272 and out of the vacuum bag set-up 250. Preferably,the surface 454 that has been prepared of the structure 452 or substratemay be exposed to the first and second vaporized chemical derivatizationcompound 268 a, 268 b containing selected functional groups. Forcomposites, the selection of the functional groups is preferably basedon the composite structure, for example. In particular, for compositestructures made of bismaleimide, it has been unexpectedly found that thechemical derivatization compound pentafluorophenol 90 (see FIG. 22)forms carbon-carbon double bond functional groups on the derivatizedsurface 400 b of the BMI (bismaleimide) (see FIG. 22). For compositestructures made of epoxy, it has been unexpectedly found that thechemical derivatization compound pentafluorophenol 90 (see FIG. 23) andforms carbon-carbon double bond functional groups on the derivatizedsurface 402 b of the epoxy (see FIG. 23).

The method 500 further comprises step 512 of heat curing the derivatizedsurface to form a high temperature hybridized molecular functional groupadhesion barrier coating. The allyl 74, maleimide 82, and hydroxyl 76hybridized molecular functional groups of the derivatized surface 400 bof the BMI (see FIG. 22) combine with the hydroxyl 76 and imide 83 (seeFIG. 23) of the derivatized surface 402 b of the epoxy (see FIG. 23) toform a high temperature hybridized molecular functional group adhesionbarrier coating.

The curing heat applied to the derivatized surface is preferably in atemperature range of from about 350 degrees Fahrenheit to about 500degrees Fahrenheit. However, the curing heat may be dependent on thebonding temperature and the bonding temperature may be dependent on theadhesive used for bonding. The curing heat may be initially ramped up toabout 350 degrees Fahrenheit at a rate of about 2 degrees Fahrenheit to5 degrees Fahrenheit per minute. The curing heat may then be held ormaintained at about 350 degrees Fahrenheit for an effective time ofabout 240 minutes. However, the effective time for holding the curingheat may be more or less depending on the bonding time and temperature,which may be dependent on the adhesive used for bonding. The derivatizedsurface may be post-cured at a higher curing heat temperature, such asin a temperature range of from about 450 degrees Fahrenheit to about 500degrees Fahrenheit. The structure with the heat cured derivatizedsurface, in the form of the high temperature hybridized molecularfunctional group barrier coating, is then preferably cooled on its ownor with a cooling element or device (not shown). Preferably, thestructure with the heat cured derivatized surface, in the form the hightemperature hybridized molecular functional group barrier coating, iscooled to a temperature below about 120 degrees Fahrenheit at a rate ofabout 2 degrees Fahrenheit to about 5 degrees Fahrenheit per minute.

After the heating and cooling curing temperature cycle, the structurewith the heat cured and cooled derivatized surface, in the form of thehigh temperature hybridized molecular functional group barrier coating,is removed from the treatment vessel. The structure with the heat curedand cooled derivatized surface, in the form of the high temperaturehybridized molecular functional group barrier coating, may then be layedup into adhesive joints upon removal from the treatment vessel and maythen be bonded to another structure. The method 500 may further compriseapplying an adhesive layer 46 (see FIG. 2C) to the high temperaturehybridized molecular functional group barrier coating. As discussedabove, the adhesive layer 46 may preferably comprise film adhesives,such as epoxies, bismaleimides, or another suitable adhesive. The method500 may further comprise joining structures together with the adhesivelayer 46. The method 500 may further comprise heat curing the adhesivelayer 46 to the joined structures 172, 176 (see FIG. 2F) to form anaircraft structural bond 180 (see FIG. 2F) between the structures 172,176.

The high temperature hybridized molecular functional group barriercoating is preferably resistant to high heat temperatures in a range offrom about 350 degrees Fahrenheit to about 2000 degrees Fahrenheit. Thehigh temperature hybridized molecular functional group barrier coatingis preferably a thermally protective, toughened adhesion coating thatmitigates effects of a hostile operating environment.

In another embodiment of the disclosure, there is provided a method ofapplying a high temperature hybridized molecular functional groupadhesion barrier coating to a surface of a composite structure, inparticular. The method is similar to method 500 discussed above but isdirected to application to a composite surface of a composite structure.The composite structure is preferably made of a polymeric materialcomprising bismaleimides (BMI), epoxies, polyimides, a combinationthereof, or another suitable polymeric material. The method comprisespreparing a composite surface of a composite structure to expose activereactive surface sites. The composite surface is preferably preparedwith one or more surface preparation treatments comprising hand sanding,machine sanding, sandblasting, solvent wiping, abrading, grit blasting,chemical cleaning, and chemical etching. More preferably, the compositesurface is prepared with hand sanding. The method further comprisespositioning the composite structure in a derivatization chamber.

The method further comprises positioning one or more liquid or solidphase chemical derivatization compounds, such as first liquid or solidphase chemical derivatization compound 264 a and second liquid or solidphase chemical derivatization compounds 264 b (see FIG. 30) in thederivatization chamber, such as a vacuum bag 256, in chemical vapordeposition vacuum bag set-up 450 (see FIG. 30). The one or more liquidor solid phase chemical derivatization compounds preferably consists ofpentafluorophenol, allyl pentafluorobenzene, tridecafluorononylmaleimide, glycidyl octafluoropentyl ether, fluorinated compounds, oranother suitable chemical derivatization compounds. More preferably, thechemical derivatization compound is pentafluorophenol.

As discussed above with respect to method 500, the method for thecomposite similarly further comprises sealing the derivatizationchamber. The method further comprises applying heat to the one or moreliquid or solid phase chemical derivatization compounds to vaporize theone or more liquid or solid phase chemical derivatization compounds. Themethod further comprises flowing the one or more vaporized chemicalderivatization compounds over the prepared composite surface. The methodfurther comprises depositing the one or more vaporized chemicalderivatization compounds on the prepared composite surface to form aderivatized composite surface having hybridized molecular functionalgroups.

As discussed above with respect to method 500, the method for thecomposite similarly further comprises heat curing at an effective curingheat temperature for an effective curing heat time the derivatizedcomposite surface to form a high temperature hybridized molecularfunctional group adhesion barrier coating. The effective curing heattemperature is preferably a temperature in a range of from about 350degrees Fahrenheit to about 500 degrees Fahrenheit. However, theeffective curing heat temperature may be dependent on the bondingtemperature, and the bonding temperature may be dependent on theadhesive used for bonding. The effective curing heat temperature may beinitially ramped up to about 350 degrees Fahrenheit at a rate of about 2degrees Fahrenheit to about 5 degrees Fahrenheit per minute. Theeffective curing heat temperature may then be held or maintained atabout 350 degrees Fahrenheit for an effective curing heat time of about240 minutes. However, the effective curing heat time for holding theeffective curing heat temperature may be more or less depending on thebonding time and temperature, which may be dependent on the adhesiveused for bonding. The derivatized surface may be post-cured at a highercuring heat temperature, such as at a temperature in a range of fromabout 450 degrees Fahrenheit to about 500 degrees Fahrenheit. Thestructure with the heat cured derivatized surface, in the form of thehigh temperature hybridized molecular functional group barrier coating,is then preferably cooled on its own or with a cooling element or device(not shown). Preferably, the structure with the heat cured derivatizedsurface, in the form the high temperature hybridized molecularfunctional group adhesion barrier coating, is cooled to a temperaturebelow about 120 degrees Fahrenheit at a rate of about 2 degreesFahrenheit to about 5 degrees Fahrenheit per minute. The method furthercomprises cooling the derivatized composite surface having the formedhigh temperature hybridized molecular functional group adhesion barriercoating.

Preferably, the high temperature hybridized molecular functional groupadhesion barrier coating is resistant to high heat temperatures in arange of from about 350 degrees Fahrenheit to about 2000 degreesFahrenheit. Preferably, the high temperature hybridized molecularfunctional group barrier coating is a thermally protective, toughenedadhesion coating that mitigates effects of a hostile operatingenvironment.

In another embodiment of the disclosure, there is provided a hightemperature hybridized molecular functional group adhesion barriercoating for a composite structure. The coating comprises one or morehybridized molecular functional groups, discussed above in connectionwith the method 500, attached to a composite surface of a compositestructure, wherein the one or more hybridized molecular functionalgroups are hybridized through a chemical derivatization process. Thehybridized molecular functional groups preferably comprise hydroxyl,maleimide, allyl, imide, or another suitable functional group. Thecoating further comprises one or more chemical derivatization compoundsattached to the one or more hybridized molecular functional groups via acondensation reaction. The chemical derivatization compound preferablyconsists of pentafluorophenol, allyl pentafluorobenzene,tridecafluorononyl maleimide, glycidyl octafluoropentyl ether,fluorinated compounds, or another suitable chemical derivatizationcompound. The coating is preferably resistant to high heat temperaturesin a range of from about 350 degrees Fahrenheit to about 2000 degreesFahrenheit, and the coating is preferably a thermally protective,toughened adhesion coating that mitigates effects of a hostile operatingenvironment. The composite structure preferably comprises a polymericmaterial such as bismaleimides (BMI), epoxies, polyimides, a combinationthereof, or another suitable polymeric material. The composite structureis preferably an aircraft structure.

FIG. 24 is an illustration of a table listing atomic compositions ofmodel chemical derivatization compounds deposited on a BMI surface. FIG.25 is an illustration of a table listing atomic compositions of elementsof the model chemical derivatization compounds deposited on an epoxyderivatized surface and a BMI derivatized surface. FIG. 26 is anillustration of a table listing the effect of derivatization on surfaceenergy for various derivatizing agents. In general, surface energychanges with derivatization were small. The longest chain fluorocarboncompound (tridecafluorononyl maleimide) reduced surface energy by 32%.FIG. 27 is an illustration of a table listing surface characterizationfor surface energy of epoxy and BMI control and derivatized surfaces.Surface energy was measured in mJ/m² (meter-Joule) per meter squared.FIG. 28 is an illustration of a table listing reactive surface sites onBMI for various derivatizing agents. The hydroxyls were shown to be thepredominant reactive functional group. Large, sterically hinderedmolecules grafted at lower areal density. The allylic (C═C) alsopresented in significant amounts. The more fluorine that was in themodel compound, the more hydroxyl was formed. FIG. 29 is an illustrationof a graph showing adhesive fracture toughness results for bonded tofunctionalized surfaces. The allylic group with (C═C) had an effect onfracture toughness and the hydroxyl (OH) group had an effect on fracturetoughness. Consuming surface maleimides had no effect on fracturebehavior. Consuming hydroxyls or allylic groups shifted failure tointerface and reduced toughness.

Disclosed embodiments of the method 500 and coating provide an adhesionbarrier coating for transforming a high temperature structure's surfaceusing hybridized or molecular functional groups which have an affinityto improve toughness, thermal oxidative degradation, high temperatureproperty retention and sustainability of the structure under hightemperature, hostile operating environments. A multifunctionalstructural barrier coating is achieved by introducing hybridizedco-polymer resistive functional groups through derivatization reactionmechanisms on the structure's surface for high temperature applicationssuch as military aircraft exhaust, engine propulsion systems, commercialwing box lining for fuel cells, and electromagnetic coatings forlightning strike protection for aircraft. In particular, the depositionof the multiple layer-by-layer (hybridized) formation ofhydroxyl-maleimide-allylic functional groups on composite (e.g.,bismaleimide (BMI) and epoxy), and metallic surfaces throughderivatization reactions has resulted in structurally toughened, hightemperature durable barrier coating adhesion bonding that may be used onaircraft structures, such as nacelles, engines, fuel tanks, and otherstructures requiring high temperature performance.

A variety of hybridized covalent functional groups may be responsiblefor successful high temperature protection and an effective structuraladhesion barrier coating for engine nacelles and other critical hightemperature aerospace structures. The adhesion barrier coating retainshigh temperature, complex hydroxyl-maleimide-allylic covalent bondingforces and secondary bonding forces which increase the long-life of thehigh temperature composite structure's surface. Primary covalent bondingforces may include the reinforced hydroxyl-maleimide-allylic functionalgroups created between the composite or metallic surface and the hostileoperating environment, which results in increased structural life cycle.Additionally, it is believed that secondary attraction forces have asignificant contribution to durable, long-term high temperaturestructural barrier protection. Secondary forces, as well as mechanicalinterlock and covalent bonding, create the final structural protection.The disclosed method 500 and coating exploit the limited mechanicalinterlocking and improved adhesion created by sanding or grit blasting.In addition, activating critical molecular co-functional groups', suchas hydroxyl-maleimide-allylic, functionality for structural BMI,epoxies, and super alloys among others, maximize the resulting hightemperature-stable, covalent layer. Such processes may produce greaterresistance to mechanical interlocking at the structural adhesion barriercoating interface. Increased surface energy due to the unique hightemperature multifunctional covalent functional groups improve thewettability of the adhesion barrier coating molecular layer andcontribute to the long-term durability, resulting in an enhancedmechanical lock between structural composite or metallic members notpreviously seen in industry.

Further, the disclosed method 500 and coating use chemicalderivatization to create a high temperature hybridized molecularfunctional group adhesion barrier coating that may act as apromoter-type layer on the structural composite surface and as a bondingagent. Multiple-hybridized-layer depositions of derivatizing hightemperature functional groups at otherwise inactive sites on thestructural composite or metallic surface create an adhesion barriercoating like multiple thin film layers (toughened high temperaturecoating adhesion barrier) that promote adhesion and result in theinnovative protective hybridized molecular layer. Such environmentallytoughened, hybridized co-polymer functional groups on the structuralsurface act as a molecular adhesion barrier coating layer and thusimprove the adhesion, which may account for increased structural, hightemperature resistance. This, in turn, may result in increased structurelife, damage tolerance, and durability.

The disclosed method 500 and coating is suitable for high temperatureenvironments that can provide adhesion promotion for structural bondingand minimize thermal oxidative degradation, without impacting structurelife, damage tolerance, and durability. The disclosed method 500 andcoating provide for a high temperature, toughened, protective coatinglayer that may be applied to many composite, metallic, or ceramicsurfaces, such as graphite/epoxy, graphite/bismaleimide,graphite/polyimide, super alloys, high temperature titanium alloys,ceramics, and other suitable surfaces. The disclosed method 500 andcoating provide for a high temperature adhesion barrier coating methodand coating for transforming a composite, metallic, or ceramicstructural surface from a limited active surface to a highly activated,high temperature derivatized adhesion barrier coating oftoughened-protective coating surface characteristics. This transformedsurface has an ability to mitigate high temperature induced structuraldamage such as loss of strength and damage tolerance. Further, themethod 500 and coating provide for a high temperature barrier coatingfor a composite structure comprising vapor phase deposition of aderivatizing compound that allows specific derivatization reaction on acomposite surface.

The disclosed method and coating may also have the potential forsignificant cost savings during manufacture and production. The savingspotential lies in the reduction of scrapping or reworking, and increasedcomposite structural damage tolerance and durability across allstructures that may experience aggressive high temperatures.

EXAMPLES

Tests were conducted with various derivatization compounds or agents onbismaleimide (BMI) composite surface substrates as follows:

Example 1

Comparative Surface Preparation Tests of Bismaleimide (BMI) Samples.Four (4) samples of bismaleimide (BMI) composite surface substrates wereprepared, tested and evaluated using various surface preparationtreatments, including: (1) “As received” which means the BMI compositesurface had no surface preparation and the BMI composite surface had noexposure; (2) “Extracted” which means the BMI composite surface waswashed with acetone solvent and then dried; (3) “Wiped” which means theBMI composite surface was hand wiped with an acetone silk cloth; and,(4) “Hand sanded” which means the BMI composite surface was hand sandedwith 60 grit aluminum oxide sandpaper until black dust has been producedand a top layer of the BMI composite matrix material was removed withthe hand sanding. An X-ray photoelectron spectroscopy (XPS) machine(Model SSX-100) obtained from Surface Sciences Inc. of Brea, Calif., wasused to measure the concentrations of carbon (C), oxygen (O), nitrogen(N), silicon (Si), and fluorine (F) present after each of the surfacepreparations was conducted. FIG. 10 is an illustration of a graph 114comparing bismaleimide surface compositions after the various surfacepreparation treatments, “As received”, “Extracted”, “Wiped”, and “Handsanded”. The results of this test showed that hand sanding of a BMIcomposite surface alone removed contaminants and also introduced carbonspecies on the surface of the BMI composite. This was likely due to theexposure of carbon fibers that are typical of carbon-epoxy composites.

Example 2

Comparative Surface Preparation Tests of Bismaleimide (BMI) Samples WithAddition of TFAA (Tetrafluoroaceticanhydride). Four (4) samples ofbismaleimide (BMI) composite surface substrates were prepared, testedand evaluated using wiped and hand sanded surface preparation treatmentsbefore and after exposure to TFAA, including: (1) “Wiped” with isopropylalcohol (IPA) which means the BMI composite surface was hand wiped withan isopropyl alcohol (IPA) soaked silk cloth; (2) “Wiped, TFAA exposure”which means the BMI composite surface was hand wiped with an isopropylalcohol (IPA) soaked silk cloth and then the wiped BMI composite surfacewas treated with chemical derivatization compound TFAA; (3) “Handsanded” which means the BMI composite surface was hand sanded with 60grit aluminum oxide sandpaper until black dust has been produced and atop layer of the BMI composite matrix material was removed with the handsanding; and (4) “Hand sanded, TFAA exposure” which means the BMIcomposite surface was hand sanded with a 60 grit aluminum oxidesandpaper until black dust has been produced and a top layer of the BMIcomposite matrix material was removed with the hand sanding, and thenthe exposed BMI composite surface was treated with chemicalderivatization compound TFAA. An X-ray photoelectron spectroscopy (XPS)machine (Model SSX-100) obtained from Surface Sciences Inc. of Brea,Calif., was used to measure the concentrations of carbon (C), oxygen(O), nitrogen (N), silicon (Si), and fluorine (F) present after each ofthe surface preparations was conducted. FIG. 11 is an illustration of agraph 116 comparing BMI composite surface compositions before and afterTFAA exposure for BMI surface compositions with surface preparationtreatments, “Wiped”, “Wiped, TFAA exposure”, “Hand sanded”, and “Handsanded, TFAA exposure”. The results of this test showed that handsanding activated the BMI composite surface toward TFAA grafting. Aftertreatment with TFAA, the results showed some carbon was consumed andoxygen and fluorine concentrations increased. The results of increasedoxygen during the TFAA derivatization process demonstrated improvedavailability of reactive species on the BMI composite surface andimproved covalent and Van der Waals forces during thecomposite-to-composite bonding process.

Example 3

Derivatization of Sanded Bismaleimide (BMI) Samples with FluorinatedDerivatization Compounds. Five (5) samples of bismaleimide (BMI)composite surface substrates were prepared, tested and evaluated usinghand sanding surface preparation treatment and exposure to variousfluorinated derivatization compounds. Each of the BMI substrate sampleswas prepared by first solvent wiping with acetone to remove handlingcontamination. Each of the BMI substrate samples was then hand sandedwith 60 grit aluminum oxide sandpaper until black dust was produced.Each of the BMI substrate samples was then wiped with acetone andKIMWIPES (KIMWIPES is a registered trademark of Kimberly-ClarkCorporation of Neenah, Wis.) followed by wiping with dry KIMWIPES untilall of the sanding debris was removed. Each of four (4) BMI substratesamples was exposed to a different fluorinated derivatization compoundvapor by suspending each of the four (4) BMI samples over a differentfluorinated derivatization compound sealed in glass vials. The four (4)fluorinated derivatization compounds included: (1) pentafluorophenol;(2) allyl pentafluorobenzene; (3) tridecafluorononylmaleimide; and (4)glycidyloctafluoropentyl ether. The fifth BMI substrate sample was acontrol and was only hand sanded and was not exposed to a fluorinatedderivatization compound. The four (4) BMI samples exposed to thefluorinated derivatization compounds and the one control BMI sample wereexposed to the same cure cycle as adhesive, that is, the temperature wasramped up from room temperature to 177° C. (degrees Celsius) over 100minutes, held at 177° C. for 240 minutes, and cooled down at roomtemperature. The BMI samples were post-cured using the followingschedule: ramped up to 227° C. over 100 minutes, held 360 minutes, andcooled down. X-ray photoelectron spectroscopy (XPS) was performed todetermine whether any bonding took place. The samples were removed fromthe glass vials, immediately placed in an X-ray photoelectronspectroscopy (XPS) sample introduction chamber (˜(approximately) 10-6torr), and allowed to outgas overnight. The samples were then gentlyheated for 20 (twenty) minutes with an ultraviolet (UV) heat lamp in theintroduction chamber to drive off any physisorbed (physically adsorbed)fluorinated derivatization compounds. The samples were grounded withcarbon tape to allow resin and fiber signals to be resolved. Floodingthe sample surfaces with low energy electrons allowed for data fromconductive fibers to be separated from nonconductive resin.

FIG. 12 is an illustration of a graph 118 comparing the following: (1)BMI surface compositions of carbon, oxygen, and nitrogen for a “SandedControl” BMI sample; (2) BMI surface compositions of carbon, oxygen,nitrogen, and fluorine for a sanded BMI sample exposed to fluorinatedderivatization compound pentafluorophenol; (3) BMI surface compositionsof carbon, oxygen, fluorine, and silicon for a sanded BMI sample exposedto fluorinated derivatization compound allyl pentafluorobenzene (therewas an unknown source of silicon in the spectra of the allylpentafluorobenzene-exposed surfaces); (4) BMI surface compositions ofcarbon, oxygen, nitrogen, and fluorine for a sanded BMI sample exposedto fluorinated derivatization compound tridecafluorononylmaleimide; and(5) BMI surface compositions of carbon, oxygen, nitrogen, and fluorinefor a sanded BMI sample exposed to fluorinated derivatization compoundglycidyloctafluoropentyl ether. The tests results showed evidence of allof the fluorinated derivatization compounds or derivatizing agents onthe BMI surface after exposure and cure cycle. The allylpentafluorobenzene-exposed sample showed significant silicon (Si) whichwas evidence of possible contamination. The allylpentafluorobenzene-exposed sample and the glycidyloctafluoropentylether-exposed sample showed no nitrogen in the sampling depth whichsuggests that the derivatizing agent itself polymerized on the BMIsurface to the extent that it covered or masked the nitrogen on thesurface and nitrogen could not be detected via XPS. XPS typically onlypenetrates the first monolayer of the surface.

The test results indicated that each of the fluorinated derivatizationcompounds was chemically bonded to its respective sanded BMI surfacesample. Exposed fibers and exposed resin surfaces appeared equallyreactive toward all of the fluorinated derivatization compounds. Thetest results seemed to further indicate that exposed fiber surfacesplayed an important role in adhesion.

Example 4

Comparative Shear Strength Tests of Bismaleimide (BMI) Samples WithAddition of Bromine and TFAA (Tetrafluoroaceticanhydride). Four (4)samples of bismaleimide (BMI) composite surface substrates wereprepared, tested and evaluated for shear strength, including: (1) a BMIsample substrate that was a “Control abraded surface” with no exposureto a derivatization compound; (2) a BMI sample substrate that was firstsanded and then exposed to bromine derivatization; (3) a BMI samplesubstrate that was first sanded and then exposed to TFAA derivatization;and (4) a BMI sample substrate that was first sanded and then exposed tobromine and TFAA derivatization. FIG. 13 is an illustration of a graph120 comparing the results of the lap joint strength or shear strength inpounds per square inch (psi) for BMI samples for “Control abradedsurface”, “Br (Bromine) derivatization”, “TFAA derivatization”, and “Brplus TFAA derivatization”. This test showed the impact of consumingfunctional groups on the bonding surface of a BMI composite surface. Thetest results showed that the consumption of units of unsaturation(double bonds) by bromination derivatization had direct impact on theshear strength of the resulting composite joint, that consumption ofhydrolyl groups through TFAA derivatization had no appreciable effect,and that a combination of bromination and TFAA treatment had anappreciably negative effect on the joint's ultimate shear strength. Thissuggested that promotion of carbon-carbon double bonds throughderivatization increased the performance of the bonded joint.

Example 5

Binding Energy Tests for BMI Samples Exposed to FluorinatedDerivatization Compounds. Binding energy tests were performed on the BMIsamples of Example 3 above that were exposed to various fluorinatedderivatization compounds. The binding energy tests were measured byX-ray photoelectron spectroscopy (XPS). XPS measures the energy ofelectrons displaced from the sample surface via X-ray impingement. Theenergy of the displaced electrons is measured as they come off thesurface. This energy represents the binding energy of the electrons onthe surface, approximately: X-ray energy in minus electron energy outplus binding energy equals zero (0).

FIG. 14 is an illustration of a graph 122 showing the results of thebinding energy test for F (fluorine) (1s) of thepentafluorophenol-exposed BMI sample. The test results showed fluorinefrom the pentafluorophenol derivatization compound bonded to fibers andbonded to resin of the derivatized bismaleimide surface. There wasevidence of hydroxyl grafting to both resin and fiber surfaces of theBMI sample. BMI adhesive appeared to adhere covalently to both resin andfiber surfaces of the BMI sample.

FIG. 15 is an illustration of a graph 124 showing the results of thebinding energy test for F (fluorine) (1s) of the allylpentafluorobenzene-exposed BMI sample. The test results showed fluorinefrom the allyl pentafluorobenzene derivatization compound bonded tofibers and bonded to resin of the derivatized bismaleimide surface.There was evidence of allyl grafting to both resin and fiber surfaces ofthe BMI sample. BMI adhesive appeared to adhere covalently to both resinand fiber surfaces of the BMI sample.

FIG. 16 is an illustration of a graph 126 showing the results of thebinding energy test for F (fluorine) (1s) of the tridecafluorononylmaleimide-exposed BMI sample. The test results showed fluorine from thetridecafluorononyl maleimide derivatization compound bonded to fibersand bonded to resin of the derivatized bismaleimide surface. There wasevidence of maleimide grafting to both resin and fiber surfaces of theBMI sample. BMI adhesive appeared to adhere covalently to both resin andfiber surfaces of the BMI sample.

FIG. 17 is an illustration of a graph 128 showing the results of thebinding energy test for F (fluorine) (1s) of theglycidyloctafluoropentyl ether-exposed BMI sample. The test resultsshowed no polymerization reaction. The glycidyloctafluoropentyl etherderivatization compound is bonded to the functional group on thebismaleimide substrate surface. There was evidence of active BMI surfaceinitiated polymerization of the epoxide group. A thick layer of polymerwas chemically bonded to the BMI surface.

Conclusions: Embodiments of the methods 150, 200, 300 and the bondedstructures produced thereby and disclosed herein provide for durablesurface modification of the composite surface or metal surface which mayresult in improved structural bonding and repair as compared to existingmethods. Further, embodiments of the methods 150, 200, 300 and thebonded structures produced thereby and disclosed herein eliminate theuse of fastener devices to secure the composite structure to the otherstructure made of the composite, the metal, or the combination thereof,or to repair the portions of the composite structure. In turn, this mayreduce overall manufacturing costs and weight of the bonded composite orcomposite/metal structure by not having to use the fastener devices.Additionally, embodiments of the methods 150, 200, 300 and the bondedstructures produced thereby and disclosed herein may enable completelybonded joints for aircraft production and repair which can providesignificant weight reduction and structural efficiency by distributingthe load to larger surface areas by eliminating the need for fasteners.Cost savings may also be achieved by the reduction of reworking ofcomposite bonded or bolted structural components. Further, embodimentsof the methods 150, 200, 300 and the bonded structures produced therebyand disclosed herein produce derivatized composite surfaces as anadhesive promoter for bonded composite and composite/metal joints andrepair. Moreover, embodiments of the methods 150, 200, 300 and thebonded structures produced thereby and disclosed herein use molecularfunctional groups as a durable adhesive promoter that may be grown oractivated on the composite or metal surface to assist composite or metaladhesion during structural bonding or repair. Environmentally durablefunctional groups on the composite structural surface can act as apotential molecular layer-adhesive promoter and thus can improve theadhesion, which accounts for increased structural bonding and repairperformance. The resulting bond is intended to have a long durabilitywithout degradation and is intended to endure for the design life of anaircraft.

Many modifications and other embodiments of the disclosure will come tomind to one skilled in the art to which this disclosure pertains havingthe benefit of the teachings presented in the foregoing descriptions andthe associated drawings. The embodiments described herein are meant tobe illustrative and are not intended to be limiting or exhaustive.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

What is claimed is:
 1. A high temperature hybridized molecularfunctional group adhesion barrier coating for a composite structure, thecoating comprising: one or more hybridized molecular functional groupsattached to a composite surface of the composite structure, wherein theone or more hybridized molecular functional groups are hybridizedthrough a chemical derivatization process; and, one or more chemicalderivatization compounds attached to the one or more hybridizedmolecular functional groups via a condensation reaction; wherein thecoating is resistant to high heat temperatures in a range of from about350 degrees Fahrenheit to about 2000 degrees Fahrenheit, and the coatingis a thermally protective, toughened adhesion coating that mitigateseffects of a hostile operating environment.
 2. The coating of claim 1,wherein the composite structure is made of a material selected from thegroup comprising bismaleimides (BMI), epoxies, polyimides, and acombination thereof.
 3. The coating of claim 1, wherein the one or morehybridized molecular functional groups comprise hydroxyl, maleimide,allyl, and imide.
 4. The coating of claim 1, wherein the one or morechemical derivatization compounds are selected from the group consistingof pentafluorophenol, allyl pentafluorobenzene, tridecafluorononylmaleimide, glycidyl octafluoropentyl ether, and fluorinated compounds.5. The coating of claim 1, wherein the composite structure is anaircraft structure.
 6. The coating of claim 1, wherein the compositestructure is made of a material selected from the group comprising oneor more of graphite (Gr)/bismaleimide, graphite (Gr)/epoxy, and graphite(Gr)/polyimide.
 7. The coating of claim 1, wherein the one or morechemical derivatization compounds is pentafluorophenol.
 8. The coatingof claim 1, wherein the one or more hybridized molecular functionalgroups attached to the composite surface are deposited on the compositesurface via chemical vapor deposition or vacuum deposition.
 9. A hightemperature hybridized molecular functional group adhesion barriercoating for a metal structure, the coating comprising: one or morehybridized molecular functional groups attached to a metal surface ofthe metal structure, wherein the one or more hybridized molecularfunctional groups are hybridized through a chemical derivatizationprocess; and, one or more chemical derivatization compounds attached tothe one or more hybridized molecular functional groups via acondensation reaction; wherein the coating is resistant to high heattemperatures in a range of from about 350 degrees Fahrenheit to about2000 degrees Fahrenheit, and the coating is a thermally protective,toughened adhesion coating that mitigates effects of a hostile operatingenvironment.
 10. The coating of claim 9, wherein the metal structure ismade of a material selected from the group comprising super alloys andtitanium.
 11. The coating of claim 9, wherein the one or more hybridizedmolecular functional groups comprise hydroxyl, maleimide, allyl, andimide.
 12. The coating of claim 9, wherein the one or more chemicalderivatization compounds are selected from the group consisting ofpentafluorophenol, allyl pentafluorobenzene, tridecafluorononylmaleimide, glycidyl octafluoropentyl ether, and fluorinated compounds.13. The coating of claim 9, wherein the metal structure is an aircraftstructure.
 14. The coating of claim 9, wherein the one or more chemicalderivatization compounds is pentafluorophenol.
 15. The coating of claim9, wherein the one or more hybridized molecular functional groupsattached to the metal surface are deposited on the metal surface viachemical vapor deposition or vacuum deposition.
 16. A high temperaturehybridized molecular functional group adhesion barrier coating for aceramic structure, the coating comprising: one or more hybridizedmolecular functional groups attached to a ceramic surface of the ceramicstructure, wherein the one or more hybridized molecular functionalgroups are hybridized through a chemical derivatization process; and,one or more chemical derivatization compounds attached to the one ormore hybridized molecular functional groups via a condensation reaction;wherein the coating is resistant to high heat temperatures in a range offrom about 350 degrees Fahrenheit to about 2000 degrees Fahrenheit, andthe coating is a thermally protective, toughened adhesion coating thatmitigates effects of a hostile operating environment.
 17. The coating ofclaim 16, wherein the one or more hybridized molecular functional groupscomprise hydroxyl, maleimide, allyl, and imide.
 18. The coating of claim16, wherein the one or more chemical derivatization compounds areselected from the group consisting of pentafluorophenol, allylpentafluorobenzene, tridecafluorononyl maleimide, glycidyloctafluoropentyl ether, and fluorinated compounds.
 19. The coating ofclaim 16, wherein the ceramic structure is an aircraft structure. 20.The coating of claim 16, wherein the one or more hybridized molecularfunctional groups attached to the ceramic surface are deposited on theceramic surface via chemical vapor deposition or vacuum deposition.